Screen printing machine



Aug. 5, 19 69 c. F. FORSLUND SCREEN PRINTING MACHINE 8 Sheets-Sheet 1Filed May 2. 1966 s NKN INVENTOR. Charles E Forslund %MI-IW7 Attorneys1.9069 c. F. FQRSLUND 3,459,125

SCREEN PRINTING MACHINE INVENTOR. Charles F Forslund I idrrorneys A g-1969 c. F. FORSLUND I. 3,45 ,125

SCREEN PRINTING MACHINE I Attorneys C..F. FORSLUND SCREEN PRINTINGMACHINE- Aug. 5, 1969 3,459,125

Filed May 2, 1966 8 Sheets-Sheet 4 Fig. /6

' At rorneys c F. FORSLUND 3,459,125

SCREEN PRINTING MACHINE I 8 Sheets-Sheet 5 Aug. 5, 1969 Filed May 2,1966 Charles E Forslund -M,%

Attorneys R E\x E m NS E m K 5 m Y N w a Q I 1 \)E Q 2 Q Ill-ll .3 r EXSCREEN PRINTING MACHINE Filed May 2, 1966 8 Sheets-Sheet emvsmoa v 1Charles F Forslund Attorneys Aug. 5, 1969 c. F. FORSLUND 3,459,125

SCREEN PRINTING MACHINE Filed May 2. 1966 8 Sheets-Sheet I ma ma F i g./3

//J F i g. /4

F i g /5 INVENTOR.

Charles F Forslund M M,%Q

Attorneys g- 5, 1969 c. F. FORSLUND 3,459,125

SCREEN PRINTING MACHINE Filed May 2, 1966 8 Sheets-Sheet 8 745 n w w F ig. /7

/57 T 1 m l5! m INVENTOR.

Charles F Forslund Attorneys United States Patent US. Cl. 10135 9 ClaimsABSTRACT OF THE DISCLOSURE A machine for imprinting boards, such asceramic wafers with a squeegee moving over a printing screen. Aturntable is formed with circumferentially spaced board receiving, boardprinting and board delivery stations, and a motor drive mechanismintermittently advances the turntable so that during each rest periodthe boards on the turntable are located at the several stations. Duringeach rest period, a locking mechanism registers one of the boards at theprinting station with the printing screen; pick up means place a newboard on the turntable at the receiving station; and an ejector at thedelivery station removes the board printed during the preceding restperiod. A motor for driving the squeegee is energized during the restperiod to move the squeegee over the printing screen and thereby imprintthe board at the printing station.

The invention relates to screen printing machines and more particularlyto those designed to screen print electronic circuit boards, ceramicsubstrates, cermets, and the like.

An object of the present invention is to provide a screen printingmachine of the character described which will automatically print smallparts as above-mentioned with precise repeatability and to very closetolerances as required for microcircuitry and components.

Another object of the present invention is to provide a screen printingmachine as described above which will produce parts of high quality inhigh speed production.

A further object of the present invention is to provide a screenprinting machine of the character described which is sturdily built toensure dependable, trouble-free operation over long production runs.

The invention possesses other objects and features of advantage, some ofwhich with the foregoing will be set forth in the following descriptionof the preferred form of the invention which is illustrated in thedrawings accompanying and forming part of this specification. It is tobe understood, however, that variations in the showing made by the saiddrawings and description may be adopted within the scope of theinventiion as set forth in the claims.

Referring to said drawings:

FIGURE 1 is a plan view of a screen printing machine constructed inaccordance with the present invention.

FIGURE 2 is a cross-sectional view of the machine taken substantially onthe plane of line 2--2 of FIG- URE 1.

FIGURE 3 is a bottom view of the machine.

FIGURE 4 is a fragmentary cross-sectional view of the machine takensubstantially on the plane of line 4--4 of FIGURE 1.

FIGURE 5 is a side elevation of a portion of the machine as suggested byline 5-5 of FIGURE 1.

'FIGURE 6 is a cross-sectional view of the portion of the machineillustrated in FIGURE 5 and is taken substantially on the plane of line66 of FIGURE 5.

FIGURE 7 is a fragmentary cross-section of a portion of the machineshown in FIGURE 6 taken substantially on the plane of line 77 of FIGURES6.

ice

FIGURE 8 is an opened out cross-sectional view of a portion of themachine as seen in FIGURE 3 and is taken substantially on the plane ofline 88 of FIG- URE 3.

FIGURE 9 is a cross-sectional view of a portion of the machineillustrated in FIGURE 3 and is taken substantially on the plane of line99 of FIGURE 3.

FIGURE 10 is a fragmentary cross-section of a portion of the machineillustrated in FIGURE 8 and is taken substantially on the plane of line1010 of FIGURE 8.

FIGURE 11 is a cross-sectional view of a portion of the machine asillustrated in FIGURE 3 and is taken substantially on the plane of line1111 of FIGURE 3.

FIGURE 12 is a fragmentary cross-sectional view of a portion of themachine taken substantially on the plane of line 1212 in FIGURE 11.

FIGURE 13 is a plan view of one of the board receiving neslts as seen inFIGURE 1 but on a somewhat enlarged sca e.

FIGURE 14 is a cross-sectional view of the portion of the machine shownin FIGURE 13 and is taken substantially on the plane of line 1414 ofFIGURE 13.

FIGURE 15 is a bottom view of the board receiving nest as seen in FIGURE13.

FIGURE 16 is a fragmentary cross-sectional view on an enlarged scale ofa portion of the apparatus taken substantially on the plane of line 1616of FIGURE 1.

FIGURE 17 is an electrical wiring diagram of the machine.

The screen printing machine of the present invention is arranged withcircumferentially spaced board receiving or loading, board printing, andboard delivery or ejection stations; a turntable 21 and a plurality ofboard receiving means 22, 23 and 24 thereon mounted for movement to andbetween the several stations; screen printing means 26 mounted at theprinting station and including a squeegee 27 (see FIGURE 2) and motordrive 28 therefor providing a pass for impressing an appropriate fluidmaterial, herein generally referred to as ink, onto a board 31positioned in registration therewith; delivery or ejection means 32removing boards from the board receiving means 2224 at the deliverystation; motor drive means shown generally in FIGURE 3 for rotatingturntable 21 and having regular periods of drive and rest for advancingthe several board receiving means in steps into succes sive registrationwith the printing station; and means phased in its operation with theturntable drive for energizing the squeegee motor drive 28 for effectinga squeegee pass during each rest period.

The several board loading, printing and ejection stations are positionedin equally circumferentially spaced intervals with the turntable mountedfor rotation concentrically of the stations, and the several boardreceiving means 22-24 are mounted in equally spaced intervals on theturntable for simultaneous registration with the station. Accordingly,the loading, printing and ejectoin cycles of the machine may take placesimultaneously to permit a high production rate of printed parts. Achain drive 33, see FIGURE 3, is provided for the delivery or ejectionmeans 32 so as to provide a cycle of operation including a pass forremoving a board from one of the board receiving means 22-24 located atthe delivery or ejection station; and the operation of the chain drive33 is phased with the turntable motor drive for effecting the boardremoval pass during each of the rest periods. Similarly, a board feedingor loading means 36, see FIGURES l and 5, is arranged to deliver anunprinted board 37 to board receiving means 22 located at the boardloading station, and to do so during the rest period of the turntable.Consequently, during this rest period a board is delivered. to theturntable at the board receiving station, a board is printed at theboard printing station, and a printed board is removed from the boarddelivery or ejection station.

The machine is here mounted on a base casting 41 providing a hub 42 uponwhich the turntable 21 is journalled by means of bearings 43, see FIGURE8. Motive power for rotating the turntable is obtained from an electricmotor 44, see FIGURE 1, which has a gear head 46 connected to a drivechain 47 in turn entrained around a drive sprocket 48 mounted on a driveshaft 49, see FIGURES 1 and 3. At the underside of the base plate 41, adrive wheel 51 is fitted on shaft 49 and which is in turn connected by apivoted link 52 to a segmental gear 53 journalled on a stub shaft 54 onbase plate 41. Accordingly, continuous rotation of drive wheel 51 bymotor 44 will be accompanied by an arcuate reciprocation of segmentalgear through alternate forward and return strokes. Segmental gear 53 hasa geared connection to the turntable which includes an overriding clutch56, see FIG- URE 10, which provides the drive and rest periods of theturntable corresponding with the alternate strokes of the segmental gear53. As will be best seen in FIGURES 3 and 8, gear 53 is enmeshed with apinion 57 mounted on a vertical shaft 58 journalled in bearings 59carried by base plate 41. A pinion 61 mounted on the upper end of shaft58 is enmeshed with a ring gear 62 provided on turntable 21. Clutch 56is incorporated in the driving connection between shaft 58 and pinion61. As will be seen in FIGURE 10, a ball carrier plate 63 is fastened toshaft 58 for rotation therewith within a cylindrical chamber 64 providedin pinion 61. A series of balls 66 is mounted in peripheral recessesformed in plate 63 and so shaped as to wedge outwardly the balls 66 intodriving engagement with the internal wall of the cylindrical chamber 64upon rotation of the shaft in a clockwise direction as viewed in FIGURE10, and to release the driving engagement between the plate and wall inthe reverse counterclockwise direction of motion of shaft 58. Thus, ondisplacement of segmental gear 53 in one direction, the drivingconnection is made to turntable 21 so as to provide the drive period,and upon reverse direction of motion of the segmental gear 53 theturntable will be in its rest period.

As an important feature of the present machine, means is provided, asbest seen in FIGURES 3, 11 and 1-2, for locking the turntable againstmovement with the several board receiving means in positive registrationwith the several stations of the machine at the conclusion of each ofthe turntable drive periods and to release the turntable for rotation atthe end of each of the rest periods. As will be best seen from FIGURES 3and 8, a cam 71 is mounted on shaft 49 and engages one end 72 of a bellcrank lever 73 journalled at its midsection on a stub shaft 7-4 providedat the underside of the base casting 41. The opposite end 76 of the bellcrank lever extends into juxtaposition to an opening 77 in the basecasting 41 adjacent to a peripheral flange 78 provided on the turntable,see FIGURES 11 and 12. A plurality of indexing blocks 79 equal in numberto the number of stations of the machine are secured to the internalface of flange 78 and are each provided with a notch or recess 81 shapedwith a taper to receive a roller 82 mounted on the upper end of an arm83 provided on the end 76 of the bell crank lever 73 and which armextends up through opening 77. A spring 86 is connected between bellcrank 73 and base plate 41 so as to constantly urge the bell crank in aclockwise direction as seen in FIGURES 3 and 12 thereby urging roller 82into a nested position in recess 81 so as to provide the locked indexedposition of the turntable. Cam 71 is provided with a pair ofsubstantially semi-circular lobes which provides a two-position locationof the bell crank with the roller swung outwardly into engagement withrecess 81 and with the roller retracted inwardly out of such engagement.

As a further feature of the present machine, each board is firmlygripped in each of the board receiving means for very preciseregistration with the screen printing means. At the same time, the boardreceiving means are arranged to open up so as to release the boardstherein at the board receiving and board delivery stations. For thispurpose, each of the board receiving means 22-24 is provided withdisplaceable detent means, see FIGURES 13, 14 and 15, which is springbiased to board securing position; and means, see cams 87 and 88, isprovided at the receiving and delivery stations for displacing thedetent means to board releasing position. With reference to FIGURES13-15, it will be seen that each of the board receiving means, heremeans 22, is provided with five spaced shoulders or stops 91, 92, 93, 94and 95, which are mounted on a supporting plate 97 in an array providinga perimeter support for a board 37 shown in phantom lines as containedbetween the several stops. In the arrangement as illustrated stops 93and 94 are spaced apart to provide a passageway 98 therebetween and stop91 is mounted for movement to and from stops 93 and 94 and also uponmovement away from such stops to drop down below the plane of plate 97so that the delivery means at the delivery station may sweep throughpassageway 98 and slide the printed boards off from the turntable. Itwill also be noted that stop is movable in slot 99 to and from stop 92,and in accordance with the present structure is moved simultaneouslywith stop 91. With reference to FIGURE 14 it will be seen that stop 91is carried at the end of a leaf spring 101 for projecting up through anopening in plate 97, and spring 101 is carried by a slide arm 102mounted for reciprocation in a guide way 103 formed in the underside ofplate 97. Stop 91 is formed with a tapered face 104 which co-functionswith a tapered edge of the opening in plate 97 through which stop 91projects, see FIGURE 14, so that upon movement of arm 102 to the left,as seen in FIGURES 13-15, stop 91 will be caused to move downwardly to aposition flush with or below the top surface of plate 97 so as torelease the board 37 from its clamped position in the stop. It will benoted that in moving downwardly, stop 91 also moves to the left, that isaway from stops 93 and 94; and contrarywise in the return movement ofarm 102, stop 91 raises and moves toward stops 93 and 94 to effectclamping of board 37. This return movement of arm 102 is here urged byspring 106 mounted in compression between the inner end 107 of arm 102and the adjacent end 108 of guide way 103.

Stop 95 is carried by a cross slide 111 mounted in a guide way 112formed in the underside of plate 97 perpendicular to and intersectingguideway 103. One end 113 of cross slide 111 is formed to enter a siderecess 114 formed in arm 102 and the end and recess are provided withtapered confronting faces 116 and 117 which cofunction to urge crossslide 111 outwardly upon inward movement of arm 102, thereby carryingstop 95 away from stop 92 simultaneously with the movement of stop 91away from stops 93 and 94. A spring 118 is mounted between an end 119 ofcross slide 111 and adjacent end of guide way 112 so as to constantlyurge slide 111 inwardly, that is, to maintain engagement of surfaces 116and 117. Each of the mounting plates 97 is secured to the turntable asby screws 121 mounted through openings in the plate so as to locate theplates in registration with the printing screen when the associatedindexing notch 81 is fixed in place by roller 82.

As will be best seen from FIGURE 1, the board receiving means asillustrated in FIGURES 13-15 are mounted on the turntable so as toposition the actuating arm 102 radially so as to locate an inner end 122of each of the arms in position to engage and be displaced radiallyoutwardly by earns 87 and 88 which are carried by a stationary centerplate 123 fixed to the hub 42 of the base casting 41, see FIGURES 1 and8. Cams 87 and 88 are located at the board receiving and board deliverystations and are formed with cam surfaces 124 shaped and positioned toengage the inner ends 122 of slide arms 102 as the board receiving meansapproach the board receiving and board delivery stations so as to movethe movable detents 91 and 95 to the open position of the boardreceiving means so as to efiect receipt and discharge of the unprintedand printed boards.

The machine may be adapted for handling different size boards by simplychanging the board receiving means assembly as shown in FIGURES 13-15.In this manner all types of circuit boards including ceramic wafers,substrates, cermets and the like can be handled for microcircuitry andcomponents; and the term circuit board as used herein is intended toinclude these several items.

Means 36 provides for the automatic feeding of boards or chips to theboard receiving nests as the latter arrive at the board receivingstation as seen in FIGURE 1. This means, as best seen in FIGURES 1, 3,5, 6 and 7, comprises a magazine 126 for holding a stack of chips 127,see FIGURE 6, to be printed and presenting an uppermost exposed chip atthe top of the stack adjacent the periphery of the turntable 21 at thereceiving station for delivery to the nest for board receiving means '22thereat; an arm 128 mounted for reciprocation between magazine 126 andthe nest 22; and means, here an air suction tip 131 carried by the armfor picking up the top exposed board at the magazine and releasing theboard at nest 22. The constantly operating vacuum pump or other sourceof reduced air pressure is connected by conduit 132 to a two-waysolenoid operated valve 133 which is in turn connected by conduit 134,see FIGURE 3, which is connected to one end of arm 128 here in the formof a hollow tube so as to communicate the vacuum source with tip 131under the control of valve 133 so that the tip is communicated with thesource when it is in juxtaposition to magazine 126 for picking up thetop exposed chips and the tip is disconnected from the source when it isin juxtaposition to nest 22 for releasing the chips to the boardreceiving means.

As will be observed, arm 128 is mounted by bracket 136 to a side member137 mounted for reciprocation on shaft 138 having one end supported inan arm 139 pivoted at 141 to the base plate 41 for arcuate upward anddownward swinging of shaft 138 during reciprocation of slide 137thereon. Slide 137 is here pivotally connected to the upper end of avertically positioned lever 142 having its lower end pivotally connectedto one end of link 143 which has its opposite end pivoted to a crank arm144 fixed by clamp 146 to the hub 147 of segmental gear 53, see FIGURES3, and 8. Accordingly upon reciprocation of the segmental gear, vacuumpick-up tip 131 will be carried reciprocally between the top of themagazine and the chip receiving nest 22; and the forward movement of thetip, that is from the magazine to the nest is elfected during the restperiod of the turntable while the reverse movement from the nest to themagazine is effected during the drive period of the turntable.

A pair of micro-switche 151 and 152 is arranged for actuation adjacentthe ends of the reciprocating stroke of arm 128 and is connectedelectrically to solenoid 153 for displacing valve 133. As will be bestseen in FIG- URES 1 and 5, liner 142 is connected by link 156 to a sliderod 157 which carries an actuator 158 for reciprocal movement betweenthe actuating arms of microswitches 151 and 152 which are mounted on asupporting plate 159 on the supporting base plate 41. Valve 133, seeFIG- URE 3, is normally biased by spring 161 to a position communicatingconduit 134 to atmospheric port 162. Upon energizing of solenoid 153 thevalve spool is displaced to the right as seen in FIGURE 3, placingconduit 134 in communication with the vacuum source conduit 132.

With reference to the electrical diagram, FIGURE 17 it will be seen thatthe rearwardly disposed switch 151 is connected in series with a relaycoil 163 and power supply lines 166 and 167. Switch 151 is normally openbut is closed by actuator 158 at the retracted position of arm 128 tothereby energize relay coil 163 and close relay switch 168. Forwardswitch 152 is normally closed and is connected to supply line 166 andrelay switch 168 which is in turn connected back to relay coil 163 so asto hold the relay energized after the closing of switch 151 and untilthe opening of switch 152. At the same time relay switch 168 isconnected to a manually controlled toggle switch 169 located at thecontrol panel of the machine and to solenoid 153 and supply line 167.Accordingly, when switch 169 is closed, the closing of switch 151 willcause actuation of solenoid 153 and the holding of the solenoid actuateduntil switch 152 is opened. Switch 152 is moved to open position byactuator 158 at the forward end of its stroke which in turn de-energizesthe relay 163 and solenoid 153 thereby causing valve 133 to shift underits spring bias to drop the chip into nest 22.

Chips in stack 126 are moved upwardly as the uppermost chip is takenfrom the top of the stack. This is here effected by a vertically setlead screw 17 1 which is connected at its lower end for rotation by anelectric motor 172. A nut 173 is threaded on lead screw 171 and isprovided with a finger 174 which enters magazine 126 to support the chipstack. Accordingly, upon rotation of lead screw 171 by motor 172, finger174 will be carried upwardly in the magazine to raise the stack of chipstherein. Preferably, nut 173 may be manually raised and lowered on thelead screw and for this purpose is provided with a slidable threadengaging part 176 which may be moved to and from lead screw 171 by amanually controlled knob 177, see FIGURE 7.

Energizing of motor 172 to raise the chip stack is under the control ofa photoelectric actuator including a light beam source 181 mounted at anelevation to throw a light beam across the top of the chip stack and onto a photosensitive receiver 182. An appropriate amplifier, not hown, isconnected between receiver 182 and motor 172 so that the motor isenergized so long as the light beam is received at an aperture atreceiver 182 and is de-energized when the uppermost chip intercepts thelight beam. Magazine 126 is here carried in a mounting bracket 184 whichmay be manually adjusted from time to time into precise positions byscrew 186.

The chip delivery means for removing printed chips from the turntablehere includes a member 187, ee FIG- URE 9, mounted at the deliverystation for reciprocation through delivery and return strokes extendingbetween the board receiving means 24 and exteriorly of the turntable fordelivery to an external chute or conveyor (not shown). Member 187 isconnected to the reciprocating drive means for the turntable formovement of the member through its delivery stroke during the restperiod of the turntable and to its return stroke during the drive periodof the turntable. The delivery mechanism includes a drive chain 188 towhich member 187 is attached and which is entrained around a sprocket191 mounted in superimposed relation to board receiving means 24 and asprocket 192 mounted exteriorly of the turntable on the upper end of avertical drive shaft 193 journalled in a bracket arm 194 fixed to thebase plate 41. A sprocket 196 is carried at the lower end of shaft 193and is connected by chain 197 to a sprocket 198 mounted on stubshaft 199depending from the underside of base plate 41. A pinion 201 connected tosprocket 198 i enmeshed with pinion 57, see FIGURES 3 and 9, so thatsprocket 198, and the chain drive connected thereto is reciprocated bythe forward and return strokes of the segment gear 53. The extent ofthis reciprocation is such as to carry member 187 from a positioninternally of the chip nest to a position externally of the turntable;member 187 being dimensioned as hereinabove indicated to sweep throughthe nest and pick up the printed chip and carry it radially across thetop face of the turntable to the outside periphery thereof for deliveryto a chute or conveyor as may be desired. The reciprocating driveconnection is such that the printed chip is removed from the turntableduring its rest period. A horizontally extending arm 202 is carried bythe upper end of bracket 194 and provides the support for the upper endof shaft 193 and sprocket 191.

The screen printing means comprises, briefly, a screen 206, see FIGURE2, mounted for positioning in superimposed relation over the boardreceiving means 23 at the delivery station; a substantially horizontallyreciprocating mount 207 for squeegee 27 positioning the squeegee forreciprocation in superimposed relation over the screen; a flood bar 209carried by the mount for reciprocation in superimposed relation over thescreen; an electric motor 211 and reciprocating drive 212 connected tothe mount for displacement thereof through forward and return strokes;and means displacing the flood bar 209 to and the squeegee from thescreen 206 during the forward strokes so as to uniformly spread the inkover the screen, and to displace the flood bar from and the squeegee tothe screen during the return stroke so as to effect a printing on thechip 31 mounted below the screen. The printing head is constructedsubstantially in accordance with the disclosure in my co-pendingapplication Serial No. 432.528 for Screen Printing Apparatus and Methodfiled February 15, 1965, and reference is made to that application for amore complete showing of the corresponding parts.

Screen 206 is here mounted in a frame 213 which is engaged by clamps 215and 216 to a sub-plate 217 which is in turn mounted on the oppositesides 218 and 219 of a main printing head supporting frame. Clamps 215and 216 are provided with manually adjustable clamping screws 220 and221 for easy and rapid attachment and detachment of the screen frame 213to the sub-plate 217. Horizontally extending lead screws 226 and 227 areeach carried in spaced upright supports 222 and 223 on plate 217 and arethreaded through and intermediately positioned nut 224 fastened by pin225, see FIGURE 4, extending through a slotted opening into engagementwith the underlying frame 213. Manually engageable knobs 228 and 229 onthe lead screws provide fore and aft adjustment of the screen, it beingnoted that the provision of such screws on the opposite sides of thescreen permits both joint and individual adjustment of these sides.Precise adjustment of the screen by lead screws 226 and 227 is effectedby loosening clamps 215 and 216 sufliciently to permit relativeadjustment between the screen frame and plate 217; and after the desiredadjustment has been effected, clamps 215 and 216 are tightened to holdthe parts in adjustment. With reference to FIGURES 2 and 4, it will beseen that the edges of screen 206 are secured to supporting members 235which are set at the four sides of the screen and are in turn mountedwithin frame 213 and are secured thereto by a series of screentensioning screws 239.

Mounting of the sub-plate 217 to the undersides of the side arms 218 and219 of the main printing frame is effected by a plurality of dovetailmounting blocks 256, 257, 258 and 259 mounted in pairs fore and aft ofplate 217, and formed to fit in mated engagement with complementarysurfaces as seen at 261 and 262 on side arms 218 and 219. Gibs as seenat 263, and tightening screws 266 and 267 therefor as seen in FIGURES 1and 4 are used to secure plate 217 in place.

The rear extremities of frame sides 218 and 219 are supported injournals 231 and 232 mounted on a cross shaft 233 which is in turnsupported at its opposite ends in vertical slide members 236 and 237carried in vertical guides 238 and 239 supported in upright position onthe base frame 41 of the machine. Slides 236 and 237 may be adjustedupwardly and downwardly by a hand wheel 241 so as to carry the rear endof the printing frame upwardly and downwardly to provide properadjustment with respect to the turntable and chip thereon to be printed.The mechanical connection between hand wheel 241 and vertical slidemembers 236 and 237 is detailed in my co-pending applicationabove-referred to and includes a geared drive to vertical lead screws240 in the housing of vertical guides 238 and 239, a common connectionbeing effected for simultaneous operation by transverse drive shaft 242.Transverse adjustment of the rear end of the printing frame may beeffected by a micrometer head 8 243 provided on shaft 233 at thevertical slide member 237.

The forward end of the printing frame may be raised and lowered by avertical set screw 244 threaded through a front side 246 of the frameand having its lower end supported on the top face of cam 87 and beingprovided at its upper end with a manually engageable knob 247 forprecise adjustment of the elevation of the frame. Fore and aftadjustment of the printing screen may be effected by screw 248 carriedby the front side 246 of the frame and threaded through an upright post249 on sub-plate 217, screw 248 having a manually engageable knob 251 atits forward end for precise manual adjustment. Accordingly, very preciseside to side, fore and aft, and up and down adjustments of the screenmay be effected. Indicator gauges 252 and 253 are mounted front and rearto show the up and down adjustments of the printing frame; indicatorgauge 254 is provided for showing the fore and aft adjustment of thescreen; and micrometer head 243 will show the side to side adjustment ofthe screen.

The present machine operates on what is normally referred to asoff-contact type printing in which a normal clearance is used betweenthe screen and the parts to be printed. As the squeegee travels over thescreen, it deflects the screen downwardly to the part to apply the inkand contact is established between the screen and the part at the tip ofthe squeegee. Proper printing pressure can be obtained by use of theadjustments above discussed. As the squeegee passes beyond the end ofthe part, the screen automatically elevates to its separated position.

With reference to FIGURES l, 2 and 4, it will be seen that squeegeedrive 28 comprises an electric motor 211 which is connected through agear head 271 to a sprocket 272 connected by chain 273 to sprocket 274mounted on a transverse drive shaft 276 extending between the side arms218 and 219 of the main printing head frame. Motor 211 is mounted on arear section of the frame so that the arms and motor and drive may beswung as a unit around shaft 233 as a center.

A pair of drive chains 277 and 278 is mounted at the outside of arms 218and 219 and extends generally horizontally with the arms around fore andaft sprockets 281 and 282 as seen in FIGURE 2. The reciprocating mount207 above referred to here consists of a pair of bushing members 283 and284 which are slidably mounted for reciprocation on horizontallyextending shafts 286 and 287 carried by arms 218 and 219 and which areinterconnected by a cross plate 288 for movement fore and aft as a unit.A pair of links 291 and 292 is pivoted at one end to bushing members 283and 284 and at their opposite ends to chains 277 and 278 so that thecontinuous motion of these chains around their supporting sprockets willbe translated into a reciprocating motion of mount 207.

Squeegee 27 is here mounted between a pair of plates 293 and 294, thelatter extending vertically above the top of the squeegee for attachmentat its opposite side edges to vertically reciprocating mounting blocks296 and 297 which are carried for vertical reciprocation upon shafts 298and 299 supported at their lower ends by brackets seen at 301 in FIGURE4.

Vertical reciprocation of blocks 296 and 297 and squeegee 27 attachedthereto at the ends of travel of mount 207 is here effected by leverarms 302 and 303 see FIG- URES 1 and 2, which extend from the pivotshafts as seen at 204 in FIGURE 4 for the forward pivoted ends of links291 and 292. As will be best seen from FIGURES 2 and 4 blocks 296 and297 will be displaced downwardly as the rearward ends of links 291 and292 pass around the forward sprockets 281 in a clockwise direction; andcontrary-wise the blocks will be displaced upwardly as the rear ends oflinks 291 and 292 pass around the rearwardly positioned sprockets 282 ina clockwise direction. Vertical adjustment of squeegee 27 relative tomounting blocks 296 and 297 may be effected by lead screws as best seenat 289 in FIGURE 2 and which are threaded through nut members 290 whichare connected to clamping screws 295 carried by the squeegee mountingplate 294, it being noted that the connection is made through slottedopenings provided in the back plate 288 of the mount. The lower ends oflead screws 289 are mounted in supporting members as seen at 309 inFIGURE 2; and the upper ends of the screws are fitted with knobs 311 toafford manual vertical raising and lowering of the squeegee.

A reverse reciprocal operation of floor bar 209 with respect to squeegee27 is effected by mounting the opposite ends of flood bar 209 on leverarms as seen at 312 in FIGURES 2 and 16. These lever arms are pivoted asseen at 313 to the lower ends of bracket 314 mounted on the slide blocks296 and 297 so that the pivoted ends of levers 312 will be carried upand down with the slide blocks. A pair of vertically set adjustingscrews 316 and 317 is threaded through arms 318 and 319 carried by theupper ends of shafts 298 and 299 and extend downwardly to hear at theirlower ends on levers 312, see FIGURES 2 and 16, intermediate their pivotpoint and flood bar 209. The levers are biased upwardly by springs 321mounted in tension between levers 312 and mounting blocks 296 and 297.Consequently, pivots 313 will move downwardly with the squeegee thuscausing levers 312 to fulcrum about the lower ends of screws 316 and317, under the urging of spring 321 to raise flood bar 209; andcontrarywise when pivots 313 move upwardly with the upward movement ofthe squeegee, levers 312 will be rotated in a counterclockwise directionas seen in FIGURE 16 so as the lower the floor bar 209. Precise settingof the flood bar in its lowermost position upon screen 206 may thus becontrolled by manually adjusting screws 316 and 317 and manuallyengageable knobs 322 and 323 are provided on the upper ends of thescrews for this purpose.

Reciprocation of the printing head assembly in properly phased relationto rotation of the turntable and its drive and rest periods is effectedby a timing cam 326 mounted on the main drive shaft 49, see FIGURE 1,and which functions to engage and actuate at the proper tlme in theoperating cycle a switch 327 to energize the printing head drive motor211. Switch 327 as will be seen from the electrical diagram FIGURE 17 isnormally open and is momentarily closed by a lobe on cam 326 and whichenergizes a relay 328 which has one of its normally open contacts 329connected to a power source and armature 331 of motor 211. The powersource is here a full wave rectifier 332 connected to power line 167 anda variable transformer 333 which is used to control the speed of thesqueegee drive. An operating knob 334 is provided at the control panel,see FIGURE 1, for operating transformer 333; and the circuit is alsocontrolled by a fuse 336 and a manually controlled master toggle switch337 connecting the transformer to the other supply line 166, toggleswitch 337 also being seen at the control panel in FIGURE 1.

As will also be seen from FIGURE 17, a normally closed switch 338 isconnected in series with switch 327 and the relay coil 328; and one ofthe relay contacts, normally open is connected in parallel across switch327. Upon closing of switch 327 by cam 326 relay 328 will be actuated toclose contacts 329 and 339; and contact 339 will lock the relay inclosed position until switch 338 opens. With reference to FIGURE 2 itwill be seen that switch 338 is mounted just to the rear of sprocket 282and in position to be actuated by the rearward end of link 291 as itpasses around sprocket 282 in a clockwise direction. Thus, squeegeemotor 211 once energized will continue to operate until the printinghead assembly is displaced to its left-hand position, as seen in FIGURE2, where switch 338 will open, thereby de-energizing relay 328 andopening contacts 329 de-energizing the armature 331 of motor 211. Anormally open manually operable switch 341 is connected from supply line166 to relay coil 328 and may be operated from the control panel inorder to manually start and stop the printing head assembly for makingnecessary adjustments in the several parts as hereinabove described.This switch will remain open during the normal automatic operation ofthe machine.

Referring to the balance of the electrical schematic diagram as shown inFIGURE 17 a master control switch 343 connects power lines 166 and 167to the sup ly lines 345 and 344. This switch is located at the controlpanel as is also a pilot light 346 which shows the power to be on andwhich is connected across the power lines in series with resistor 347.Also connected across power lines 166 and 167 is a thyrector 348 and afull wave rectifier 349 which supplies power to the field windings 351and 352 of the turntable motor 44 and the squeegee drive motor 211.

Preferably a manually operable speed control is provided for theturntable drive motor which in turn controls the operating speed of theoverall cycle of the machine. As shown in FIGURE 17, power for thearmature 353 of the turntable drive motor is received from a full waverectifier 354 which is in turn energized by a variable transformer 356,the control knob 357 of which will be seen at the control panel inFIGURE 1. Transformer 356 is connected to the power supply line througha fuse 358 and a manually controlled toggle switch 359 which will alsobe seen at the control panel. A capacitor 361 is here connected acrossarmature 353. Other switches 362 and 363 are provided at the controlpanel for operating the chip magazine lift motor 172 and for turning onand off of the vacuum pump connected to the vacuum pick-up tip 131 ofthe feed mechanism.

I claim:

1. In a machine for screen printing circuit boards and including aturntable having a plurality of board receiving means mounted thereon,board loading means and motor operated screen printing means and boardejection means circumferentially disposed of said turntable at boardloading and board printing and board ejection stations respectively,motor driven means for rotating said turntable and having regularperiods of drive and rest and being correlated with said board receivingmeans to advance the latter in steps into successive registration withsaid printing station, and means phased in its operation with said motordriven means for energizing said motor operated printing means forimpressing ink onto a board registering therewith, wherein said boardreceiving means comprises, detent means carried by said turntable fordetermining the position of said boards thereon and having radiallyextending arms displaceable radially outwardly to a board releasingposition, spring means biasing said arms to board securing position, andcamming means at said board loading and board ejection stations forengagement with and outward displacement of said arms.

2. A machine as defined in claim 1, wherein said board receiving meansand detent means comprises a plurality of fixed and movable stopspositioned for engaging the periphery of said board and said moveablestops being biased for clamping said board, and said arms beingconnected for displacement of said movable stops away from said boardperiphery.

3. A machine as defined in claim 2, wherein said stops are mounted formovement of boards radially of said turntable into and out of engagementwith said stops at said loading and ejection stations.

4. A machine for screen printing circuit boards and havingcircumferentially spaced board loading and board printing and boardejection stations which comprises; a turntable and a plurality of boardreceiving means thereon mounted for determining the position of boardson said table and for movement of said means to said stations; screenprinting means mounted on said printing station and including a squeegeeand a motor drive therefore providing a path impressing ink onto a boardpositioned in registration therewith; ejection means for removing saidboards from said board receiving means at said ejection station; a motordriven means for said turntable having a motor and a segmental gearhaving a geared connection to said turntable and reciprocating drivemeans connecting said motor and gear for driving said gear throughalternate forward and return strokes and a clutch mounted in said gearedconnection and providing regular periods of drive and rest correspondingwith alternate strokes of said gear and being correlated with said boardreceiving means to advance the latter in steps into successiveregistration with said printing station; and means phased in itsoperation with said motor driven means for energizing said squeegeemotor drive for effecting said squeegee pass during each rest period.

5. A machine as defined in claim 4, a magazine for holding a stack ofboards to be printed and presenting an exposed board at the end of thestack adjacent the periphery of said turntable at said loading stationfor delivery to said board receiving means thereat, an arm mounted forreciprocation between said magazine and board receiving station, andmeans carried by said arm for picking up said exposed board at saidmagazine and releasing said board at said board receiving means, saidarm being connected to said reciprocating drive means for delivery ofsaid board to said board receiving means during said rest period and forreturn movement of said arm during said drive period.

6. A machine as defined in claim 4, means providing a plurality ofindexing notches on said turntable circumferentially distributed thereonaccording to said stations, a roller mounted for reciprocation into andout of seated engagement with one of said notches brought intoregistration therewith for precisely setting and locking the rotationalposition of said turntable, cam drive means connecting said roller tosaid motor for movement of said roller to said seated position at theconclusion of each turntable drive period and withdrawing said rollerfrom said seated position at the end of each rest period.

7. A machine as defined in claim 4, wherein said ejection meanscomprises, a member mounted at said ejection station for reciprocationthrough delivery and return strokes extending between said boardreceiving means and exteriorly of said turntable and being formed andpositioned to engage and remove a board during its delivery stroke, saidmember being connected to said reciprocating drive means for movement ofsaid member through its delivery stroke during said rest period andthrough its return stroke during said drive period.

8. A machine as defined in claim 7, a chain drive at said ejectionstation including a sprocket mounted in superimposed relation to saidboard receiving means and a sprocket mounted exteriorly of saidturntable and a chain entrained on said sprocket, said member beingcarried by and depending from said chain, and drive means connectingsaid chain drive to said segmental gear for displacing said memberthrough its delivery and return strokes upon reciprocation of saidsegmental gear.

9. A machine for screen printing circuit boards and havingcircumferentially spaced board loading and board printing and boardejection stations which comprises, a turntable and a plurality of boardreceiving means mounted thereon for determining the position of board onsaid turntable and for movement of said means to said stations, screenprinting means mounted at said printing station and including a squeegeeand a motor drive therefor providing a pass impressing ink onto a boardpositioned in registration therewith, ejection means for removing saidboards from said board receiving means at said ejection station, motordriven means for rotating said turntable and having regular periods ofdrive and rest and being correlated with said board receiving means toadvance the latter in steps into successive registration with saidprinting station, means providing a plurality of indexing notches onsaid turntable one associated with each of said board receiving means, aroller mounted for reciprocation into and out of seated engagement withsaid notches upon rotation of said turntable for locking the rotationalposition of said turntable and functioning when in engagement with anotch to locate its associated board receiving means in preciseregistration with said screen printing means, drive means connectingsaid roller and motor driven means for movement of said roller to saidseated position at the conclusion of each turntable drive period andwithdrawing said roller from said seated position at the end of eachrest period, and means phased in its operation with said motor drivenmeans for energizing said squeegee motor drive for effecting saidsqueegee pass during each rest period.

References Cited UNITED STATES PATENTS 382,637 5/1888 Curtis 192-45521,749 6/ 1894 Williams. 1,929,549 10/ 1933 Glass 101-408 1,963,8506/1934 Johnston 101-43 2,966,115 12/1960 Arelt 101-126 3,263,603 8/1966Fuchs 101-123 ROBERT E. PULFREY, Primary Examiner CLIFFORD D. CROWDER,Assistant Examiner US. Cl. X.R.

